It is well known in the art of forming continuous glass fiber, filaments, strands and/or rovings, the latter comprising as many as hundreds of individual glass fibers gathered together and treated as a unit, to pull those glass fibers from the forming bushing by leading them around the exterior of a rotating tube to build up upon the tube a considerable mass of the fibers so that they later can be utilized for weaving, etc. As the length of strand or roving builds up upon the tube, the tension of pulling the hundreds of glass fibers from their forming bushing creates inwardly compressive force on the mass of fibers and thus upon the tube about which they are wrapped. This inward force is transferred, of course, to the surface of the device upon which the tube is mounted for rotation.
In order to form satisfactory "packages," i.e., masses of continuous groups of filaments such as strands or rovings on such a sleeve, it is essential that several criteria be observed.
First, it is necessary that the mechanism for mounting and rotating the package tube be able to receive and hold the tube and be so designed as to permit the removal of a loaded tube.
Second, it is essential that the tube upon which the strand or roving is being wound shall not move axially during the winding process because any such movement will disturb the "lay-up" on the tube and may result in over-wrapping turns on the tube which would create snarls and entanglements at the time of removal of the strand or roving from the tube for subsequent processing operations such as weaving and the like.
Third, it is critically essential that the tube and the body of strand being built up thereupon shall be maintained in true cylindrical configuration so that the lineal speed of pulling of the strand or roving and the hundreds of fibers of which it is comprised will be constant and will not have any "beat frequencies" which would result if, for example, one portion of the package tube on which it is being wound had a greater or lesser radius than some other portion.
Fourth, the desired fixed diameter of the package tube and the mass of strand or roving being built up thereupon must be uniform from one end of the tube to the other, i.e., even though the surface remains truly circular. If, for example, the diameter at the center of the length of the tube is greater than that at its ends, when the strand is led back and forth across the center portion the lineal speed of the strand will be increased and decreased, which also tends to interfere with the pulling operation.
It previously has been suggested that package tubes of this type may be mounted upon collets comprising expansible balloon-like bladders of the like which can be expanded radially outwardly by air under pressure to frictionally engage the inner surface of the tube to transmit torque to the tube, to endeavor to hold it against axial movements, and to hold it in its fully cylindrical shape. Unfortunately, if simple balloon-like bladders are utilized, the pressure along their axial length is not uniform; they may bulge to a lesser extent at various axially spaced portions of their circumference; they will not necessarily hold the entire axial length of the tube to the constant desired diameter.
It also has been suggested that such an expansible device might be designed having axially extending bars mounted on its periphery, which would be moved outwardly into contact with the inner surface of the sleeve by air pressure admitted to individual expansion chambers located radially inside of the bars. If each bar is provided with its own expansion chamber, it is then difficult to be certain that all of the bars are pressed outwardly with the same force and maintained out at their preferred diameters to satisfactorily contact and hold the package tube.
Examples of the foregoing devices are illustrated in the U.S. Pat. Nos. 3,458,150; 3,904,144; 3,414,210; 3,273,817; and others.
It also has been suggested that package tubes of the type herein discussed adequately may be held in place and maintained in true cylindrical configuration by the utilization of a mounting collet having radially movable support bars which are radially moved outwardly into contact with the inner surfaces of the packages and held against the packages by the centrifugal force created by the relatively high-speed rotation of the packages. In such devices, however, yet another problem may exist.
When the strand or roving first is led to the surface of the sleeve-like package, the circumference of the sleeve and its R.P.M. determine the lineal speed of pulling of the strand or roving and thus of the hundreds of individual glass fiber filaments of which it is comprised. As the body of strand or roving builds up upon the sleeve and upon itself, the effective diameter and, as a result, the lineal speed of the strands being wrapped will all increase. In order to maintain constant the diameters of the individual filaments being pulled from the forming bushing and thus satisfactory formation, as well as a constant weight per lineal dimension of the strand or roving, it has been learned that it is necessary gradually to decrease the R.P.M. of the package as it builds up. This may result in reducing the rotational speed of the package in a factor of as much as 2:1 between the beginning of the formation of an individual package and its completion. As a result, the package may be rotated at a speed as low, for example, as 400-500 R.P.M., which, of course, greatly reduces the centrifugal force acting to hold the package-contacting elements outwardly.
To overcome this problem, it would be necesssary greatly to increase the mass of the package-contacting elements so that at slower rotational speeds they would still adequately maintain contact with the interior surface of the package being wound. A considerable increase in the mass of these elements, of course, greatly increases the weight of the unit and may introduce excessive centrifugal force against the inner wall of the package during the initial portion of its rotation at a higher rotational speed. The determination, thus, of the mass of the package-contacting elements becomes important as well as the provision of some means for positively limiting the radially outward distance to which the package-contacting elements can be moved regardless of the rotational speed of the collet.
In general, devices suitable for the purposes discussed above are called "expansible collets" and will be so denominated herein.
It is, therefore, the principal object of the instant invention to provide a collapsible collet for a tubular sleeve onto which a very substantial length of a continuous filament, strand, or roving, or the like, is to be wrapped, the collet comprising a plurality of axially extending movable elements which are thrust outwardly into tight contact with the inner surface of the sleeve for delivery of rotary torque thereto and in order to hold the sleeve in cylindrical shape.
It is yet another object of the instant invention to provide an expansible collet for a tubular sleeve which will enhance the tubular sleeve with sufficient force to restrain it against axial movement, to apply rotational torque thereto, to maintain it in true cylindrical shape during substantial changes in its revolutions per minute as necessary to compensate for the increase in the diameter of the package being would thereon thus to maintain a constant lineal speed of the material being packaged.
It is yet another object of the instant invention to provide a collapsible collet having positive mechanical means for the engagement of the inner surface of the tubular sleeve mounted thereon, the mechanical means being pneumatically moved from an inner, reduced diameter position to a larger diameter position and held in such larger diameter position with sufficient force to maintain a firm grip of the tubular sleeve regardless of is revolutions per minute, while maintaining the sleeve in true cylindrical configuration.